Internal combustion engines running on hydrocarbon fuels usually require a spark plug to trigger combustion. Spark plugs are understood to be essentially comprised of two electrodes separated by an insulator and some form of a support structure which can be air-tightly fitted in a combustion engine, such that the two electrodes are immersed in the atmosphere of the combustion engine. The electrodes are at different electrical potentials, most often the electrode in contact with the engine housing acts as ground and the potential of the central electrode is periodically raised to a higher potential, thereby generating a spark, however, a reversed polarity of the applied potential is also possible. The spark dissociates and activates the molecules of the gas located in the gap between the respective surfaces of the electrodes, thereby creating a plasma of activated gas atoms or radicals, which then ignites the air and hydrocarbon containing fuel mixture in the combustion engine. It should be clear from the foregoing that to ensure that the combustion device is working satisfactorily, it is of importance that the spark gap width between the electrode surfaces is essentially kept constant, the electrode surfaces are clean, the electrodes are separated by adequate insulation, and in the absence of electrically conducting surfaces detrimental to plasma generation. To meet these requirements the build-up of deposits on the electrode surfaces and on the adjacent insulator surfaces, as well as surface layers of oxidation products of the electrode materials are to be avoided, all of which are likely to lead to misfiring and/or irregular firing of the spark plug. It is known that over-heating of the electrode surfaces can lead to oxidation and spark erosion, on the other hand, under-heating may lead to carbonaceous deposit formation. Such deposits are frequently encountered in the course of operating conventional spark plugs, and are usually formed by build-up of soot, pyrolytic carbon or high melting point hydrocarbons such as waxes, which in turn may be the consequence of incomplete combustion, temperature variations within the engine, fuel mixtures having inadequate composition, and such like. The above deposits are particularly deleterious, affecting adversely the firing of the spark plug electrodes and hence the combustion of the lean fuel-air mixtures which is often utilized nowadays.
Oxidation and spark erosion of the electrode surfaces will also undermine the efficiency and lifespan of the spark plug. Furthermore, misfiring of a spark plug may result in the production of nitrous oxides, as well as oxidation of some fuel additives which may then result in toxic by-products leading to undesirable and noxious components in the exhaust gases.
There have been several known methods to improve the performance of spark plugs. One of such developments have been modifications made to spark plug geometry. Such modifications are described, for example, in U.S. Pat. No. 4,015,160 issued to Lara et al. on Mar. 29, 1977. Other attempts have been directed to improving ionization in the gas phase by changing the geometry of the spark gap in a particular manner, such as for example, described in U.S. Pat. No. 3,911,307 issued to Goto et al. on Oct. 7, 1975. Spark plug electrodes made of an oxidation resistant titanium compound dispersed in a noble metal containing matrix are taught by Kanemitsu Nishio et al. in U.S. Pat. No. 4,427,915 issued on Jan. 24, 1989, which is another example of tackling the problem of spark erosion due to oxidation. It is noted, however, that the spark plug electrodes described in U.S. Pat. No. 4,427,915 are likely to be costly to manufacture.
In another approach to improving spark plug performance, the likelihood of formation of carbonaceous deposits and oxidation on and between sparking surfaces is reduced by injecting hydrogen gas, oxyhydrogen gas, oxygen or atomized water into the spark gap between the electrode surfaces. There are other known methods for introducing gases such as hydrogen, utilizing injection devices, for supplementing the fuel combustion efficiency of an internal combustion engine. A device for introducing hydrogen and oxygen gases into the spark gap is described in U.S. Pat. No. 4,343,272 issued to A. C. Buck on Aug. 10, 1982. One of the attendant difficulties in this approach is that injection of the gases needs to be carefully synchronized with engine operation, furthermore separate gas containers need to be accommodated. All in all, gas injection through a nozzle operated in conjunction with a spark plug requires a fairly complex system.
It is noted that engines designed to run on only hydrogen as fuel, generated by heating metal hydrides are also known, but such systems do not require conventional spark plugs, and at any rate, hydrogen engines represent a completely different approach to the problem.
A process utilizing LaNi.sub.5 H.sub.6 in a spark plug is described in SU 1368936, issued in the former Soviet Union on Jan. 23, 1988, to Kudryash et al. The role of the metal hydride is to provide nascent hydrogen diffusing through a ceramic oxide barrier into the spark gap to enhance ionization when the spark is struck. However, nascent or atomic hydrogen in amounts which is sufficient to have a notable effect on the efficiency of ignition in the spark plug is generated only when the engine is hot. Moreover, the atomic hydrogen is likely to recombine in the spark gap to molecular hydrogen before it can be utilized for increasing the spark plug efficiency. The spark plug of SU 1368936 requires a separate heater to generate hydrogen from the hydride when the engine is cold. The hydrogen is generated as the engine and the spark plug attached to it, attain sufficiently high temperature, and not limited to instances of ignition of the fuel mixture. In other words, a substantial portion of the hydrogen generated by the metal hydride is not used in the sparking step, thus the hydrogen source is likely to get exhausted early in the life of the spark plug.
The object of the present invention is to utilize a metal hydride for enhancing the efficiency and control of hydrocarbon fuel ignition in a spark plug without relying on engine heat or without a need for an additional heater and a ceramic oxide barrier to be incorporated in the spark plug.